<template>
	<ul class="list" ref="list">
		<li class="item" 
		v-for="item of letters" 
		:key="item"
		:ref="item"
		@touchstart.prevent="handleTouchStart"
		@touchmove="handleTouchMove"
		@touchend="handleTouchEnd"
		@click="handleLetterClick">
			{{item}}
		</li>
	</ul>
</template>

<script>
	export default {
		name: 'CityAlphabet',
		props: {
			cities: Object
		},
		computed: {
			letters: function(){
				const letters = []
				for(let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		data: function(){
			return {
				touchStatus: false,
				startY: 0,
				timer: null
			}
		},
		updated: function(){
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods: {
			handleLetterClick: function(e){
				this.$emit('change', e.target.innerText)
			},
			handleTouchStart: function(){
				this.touchStatus = true
			},
			handleTouchMove: function(e){
				if(this.touchStatus){
					if(this.timer){
						clearTimeout(this.timer)
					}
					this.timer = setTimeout( () => {
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor((touchY - this.startY) / 20)
						if(index >= 0 && index < this.letters.length){
							this.$emit('change', this.letters[index])
						}				
					}, 16)	
				}
			},
			handleTouchEnd: function(){
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display: flex
		flex-direction: column
		justify-content: center
		width: .4rem
		position: absolute
		top: 1.58rem
		right: .06rem
		bottom: 0
		text-align: center
		.item
			height: .4rem
			line-height: .4rem
			color: $bgColor
</style>